Somites are the metameric precursors of the vertebrate axial skeleton and musculature. Mutations in Notch pathway genes perturb somitogenesis in mice and zebrafish and are associated with congenital vertebral defects in humans. A second phenotypic class in which only the anterior or cervical region is malformed is represented by our before eight mutant in zebrafish and by Klippel-Fiel syndrome in humans. Using zebrafish, I study the genetic control of somitogenesis along the anterior/posterior axis of the embryo. Of particular interest is a Notch-dependent cellular oscillator that regulates somite formation. A contemporary problem in biology, at the interface between developmental biology and systems theory, is understanding the relationship between genetic networks, their self-organizing and emergent properties (such as oscillations) and the creation and evolution of multi-cellular organization. The somitogenesis oscillator provides an accessible system to address these questions. Here, I propose a reverse genetic approach to isolate new genes involved in somitogenesis. I will use a new zebrafish oligo-array representing 14,000 unique genes to determine the expression profiles of tissue from wild-type and mutant embryos in which the somitic mesoderm fails to differentiate. Genes specifically down-regulated in the mutants will be examined using antisense inhibition to ascertain their function in the embryo.